The present invention relates to refrigeration apparatus of the type generally referred to as a water chiller. With still more particularity, the present invention is directed to apparatus and a method for reducing the noise caused by refrigerant gas flow and its interaction with mechanical components in a water chiller of the centrifugal type.
Centrifugal chillers are large mechanical apparatus which in the simplest sense, are comprised of the same components as small air conditioning and refrigeration systems. In that regard they include a serially connected compressor, condenser and evaporator together with apparatus for metering refrigerant from the condenser to the evaporator. In the case of a centrifugal water chiller, a centrifugal compressor compresses refrigerant gas and discharges it to the system condenser which is typically a shell and tube heat exchanger. The acoustically energetic stream of compressed refrigerant gas delivered from the compressor to the condenser is cooled therein, typically by water supplied from a cooling tower or the local water supply. The gas condenses to liquid form in the condenser cooling process.
Once it has been condensed, the relatively high pressure system refrigerant is directed out of the condenser to a metering device where an expansion process occurs. The expansion process causes still further cooling of the system refrigerant as well as a reduction in the pressure thereof. The now relatively low pressure and much cooler system refrigerant is directed into the system evaporator where it is brought into heat exchange contact with a medium, such as water, which is chilled to a predetermined temperature by its heat exchange contact with the cooled system refrigerant. The chilled water is most typically used in a building air conditioning application or in an industrial process. System refrigerant, after having been vaporized in its heat exchange contact with the water in the evaporator, is returned to the compressor portion of the chiller where the process starts anew.
It is known both in practice and in the patent art to inject liquid refrigerant directly into the compressor portion of a centrifugal chiller at a location where system refrigerant is undergoing compression. In that regard, the existence in commercial practice of the injection of liquid refrigerant behind an impeller hub plate in a centrifugal compressor is noted as are arrangements such as those taught in U.S. Pat. Nos. 2,786,626 and 4,695,224. These patents are similar in that they both teach the injection of liquid into the multiple stages of a centrifugal compressor to achieve interstage cooling of the refrigerant undergoing compression. Such cooling of the refrigerant undergoing compression is said to improve the performance and life of the centrifugal compressor.
U.S. Pat. No. 4,419,865 teaches a screw compressor-based refrigeration system in which liquid refrigerant is directed into the line connecting the system's screw compressor to its oil separator in order to cool the mixture of oil and system refrigerant discharged from the compressor prior to its entry into the oil separator. The patent teaches that such cooling is necessary to enable the oil separator to effect the necessary, more complete separation of the relatively very large amount of oil which is carried out of screw compressors as compared to compressors of other types.
As government regulations and building owners become more demanding with respect to equipment noise levels, the need exists to quiet equipment such as centrifugal chillers to the extent possible without significantly affecting the performance or efficiency of such equipment. One source of noise in centrifugal chillers is noise which develops and is radiated by and from the chiller as the acoustically energetic, high velocity stream of refrigerant gas is discharged from the compressor portion of the chiller and is delivered to and into the system condenser where it interacts with the intervening piping and the condenser's mechanical components and structure. As such, means by which to reduce the noise associated with refrigerant gas as it passes from the compressor portion of a centrifugal chiller to and into the system condenser, without significantly affecting compressor performance and efficiency, represents an advantageous development in the centrifugal chiller art.